Nissan Repair: knock sensor, nissan altima, rod bearings

Question
My check engine light is on. I went to autozone to get a diagnostic on my 1997 Nissan Altima 2.4 GLE. The code came out to be a KNOCK SENSOR. What is knock sensor, and what do I have to do to fix it?  

Answer
Brian,

The knock sensor is a sonic sensor that monitors shockwaves in the water jacket of the engine.  It senses when the engine pings.  That is, pre-ignition when the timing is too far advanced.  The knock sensor tells the computer that the engine is pinging and the computer retards the timing.  These sensors fail over time and when they do the computer goes into limp mode.  This a pre-programmed timing map where the timing will not advance far enough to cause pinging.  So, the engine performance will be down because the timing will be retarded and fuel economy will suffer.  But, the good news is that the engine will not sustain damage from having the timing too far advanced.  Too much timing will cause pinging and this will cause the rod bearings to be damanged and could cause a spun rod bearing.  So, it is just a matter of purchasing a knock sensor and replacing the old one.  Disconnect the battery while you do the replacement and your code should clear and you should be back in business.